The human spine frequently requires surgery to repair deformities or injuries. Spinal problems may be caused by a trauma to the spine received during an accident, excessive strain or stress on the spine from physical activities, a sedentary lifestyle and poor posture that may place abnormal pressure on the spine, disease or a variety of other reasons. Spinal fusion is a common surgery intended to alleviate pain caused by these spinal deformities or injuries.
The spinal fusion procedure generally includes removing a disk, packing a bone graft between vertebrae and placing a spinal implant, such as screws attached to a plate, rod or cage, to fuse elements of the spine together. Once the disk is removed and the bone graft is placed between the vertebrae, the bone graft will fuse to the vertebrae over a period of several months following the surgery.
The purpose of the plate is to stabilize the vertebrae until the bone graft has become fused to the vertebrae. The plate is positioned to extend between at least two vertebrae. The plate is attached to screws anchored in each of the adjacent vertebrae, thus immobilizing the desired portion of the spine. The plate is anchored to the screws either on the front, anterior, or back, posterior, sides of the vertebrae.
Procedurally, anterior, or entry from the neck region of the patient, cervical vertebra surgery provides the surgeon with optimum access to the entire intervertebral disk. Posterior, or entry from the back of the patient, surgery is less preferred since access to the disk is restricted. Once the anterior cervical discectomy, or removal of the cervical disk, is completed, the bone graft is placed into the space between the vertebrae previously occupied by the disk. The patient is then positioned for anterior cervical fusion, or placement, of the plate.
One particular anterior cervical fusion technique is accomplished by securing fixation screws in the vertebral body. Rods and/or plates are then engaged between the screws in superior and inferior vertebral bodies. Normally, two screws are placed in each body. Therefore, two rods and/or plates are needed between the vertebrae. The rods and/or plates and screws thereby stabilize the cervical vertebrae and provide time for the vertebrae and bone graft to fuse into a solitary unit.
However, anterior cervical fusion has caused increased operative morbidity due to the very difficult nature of the procedure. Moreover, many of the anterior cervical fusion techniques have problems of potential risk to a surrounding vascular network and in completely clearing the adjacent spinal canal. Furthermore, most of the anterior cervical fusion techniques rely on support from the vertebral body only and therefore cannot be used in an extremely osteoporotic spine because vertebral body strength is not sufficient.
Several plating systems have been developed for anterior internal fixation of the spine. Among these plating systems, a Syracuse I-plate provides a number of differently sized I-shaped plates which are engaged across a burst fracture. However, the Syracuse I-plate does not allow for compression or distraction of a bone graft between the superior and inferior vertebrae. A Stafix plating system, provided by Duma International of Taipei, Taiwan, includes a plate that has a number of screw holes and a single screw slot. The Stafix plate permits quadrilateral placement of bone screws, but not compression or distraction. Moreover, the Stafix plate, as with the above-mentioned anterior plates, cannot provide rigid or semi-rigid fixation using bone screws or bone bolts.
Thus, a need exists for a vertebral screw arrangement that obtains the benefits while overcoming the disadvantages of prior procedures and systems.